I still shaking my head on this one. On April 17, I sent my return and a check for a 4-figure tax owed. Last week, I got a letter notifying me of a penalty and interest for a late payment. I called, and tell them I sent the payment in on the correct date, with my return. I was informed that, just like the bank, if you mail the check on the due date, it won't get posted for several days after that, and your payment will be late.

Anyone else go through this? I'm inclined to dispute this; any idea of the best way to do that? The amount is small, but it's a principle.